Dracaena, Vandelli ex Linnaeus, 1758
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publication ID |
https://doi.org/ 10.11646/zootaxa.3985.3.1 |
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publication LSID |
lsid:zoobank.org:pub:46DE9DD6-55E3-4BF5-A2AF-A058A0294A72 |
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persistent identifier |
https://treatment.plazi.org/id/F37C6616-FFD3-FFDC-A0B6-FF65D917FD41 |
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treatment provided by |
Plazi |
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scientific name |
Dracaena |
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Dracaena View in CoL spp. ( Asparagaceae )
Dracaena is a genus of about 100 species of trees and succulent shrubs, the majority of which occur in Africa. It is placed in the phylum Asparagales , family Asparagaceae , subfamily Nolinoideae (Stevens 2012) , although it has been placed in Dracaenaceae (now subsumed in Nolinoideae ), Agavaceae (now subfamily Agavoideae of Asparagaceae ), Ruscaceae (subsumed within Nolinoideae ) and Liliaceae (an unrelated Holarctic family). Here, the nomenclature of Govaerts (2013) is followed for the eight or so identified species recorded as food plants in mainland Africa ( Table 1 View TABLE 1 ). However, early records are difficult to interpret given the changes in our knowledge of the genus; e.g. Dale & Greenway (1961) recognised four species from Kenya, but Beentje (1994) recognised eight.
Dracaena steudneri (Figure 1.2, 2) is commonly planted as an ornamental in East Africa ( Gardner 1950). Dracaena fragrans has been used as a hedge plant in Uganda ( Thomas 1950), but Dale & Greenway (1961, p. 9) indicate that D. steudneri was ‘at one time assigned to D. fragrans ’, so records from this host may need confirmation. Although MJWC has recognised and probably only collected off D. steudneri in eastern Africa, TCEC has recognised and collected off several other species or apparent species in Tanzania, Malawi and Zambia, including D. mannii , D. camerooniana (Figure 1.3) and D. laxissima (Figure 1.2). In his experience, there appear to be at least two morphological species within D. laxissima , one with small leaves with wavy edges and pink flowers, the other with larger, smooth edged leaves and white flowers, which grow together in the Kihansi Gorge, Udzungwa Mountains, Tanzania. Similarly, there appear to be two species on the Rondo Plateau, south-eastern Tanzania, one like D. mannii , the other more like D. laxissima . In the Misuku Hills, north Malawi, TCEC found three phenotypes, two of which would be identified as D. laxissima . Once the taxonomy of this group is clearer, some of our records will need re-evaluation.
The situation in Madagascar is not clear. At the moment, most of the Dracaena spp. of Madagascar are treated as D. reflexa with 13 subspecies, all of them showing a high level of morphological diversity. Buerki et al. (2009) attempted a molecular analysis, which revealed three clades of Madagascan Dracaena, which do not align with recognised names. Clades A and C occur in the north of Madagascar, clade A principally in humid evergreen forest (Montagne d’Ambre and humid zones of the northern part of Daraina) whereas clade C occurs in semi-deciduous to deciduous forest (Ankarana and dry zones of the southern part of Daraina). Clade B covers a much larger area in central and southern Madagascar, with two biogeographic groups, B 1 in low to mid-elevation evergreen forest of the east coast of the island, and B2 throughout the southernmost part of Madagascar in semi-deciduous to dry forests. Buerki et al. (2009) conclude that their results highlight the difficulty of defining evolutionarily significant units in Malagasy Dracaena, and indicate the complex speciation processes taking place. In northern Madagascar, TCEC found A. boseae (Saalmüller) and Artitropa sp. SCC01 on a small ‘species’ resembling D. mannii , and Artitropa sp. SCC03 on a much larger ‘species’ more like D. steudneri . Based on the work of Buerki et al. (2009), most of our records of Dracaena sp. as food plants of Artitropa spp. in Madagascar are likely to refer to Clade A, based on location and habitat.
Dracaena steudneri grows to be a relatively large tree, although Artitropa spp. early stages tend not to be found on the larger plants. MJWC has noted that it (and probably other Dracaena spp.) shows considerable phenotypic plasticity, as shown in the following casual observation. Two apparently identical small cuttings were purchased from a Nairobi street-side plant seller; one was planted in the ground in full sunshine, while the other was planted in a pot and kept in shade. After three years it was not obvious that these could be the same species: the plant grown in full sun was robust with many large, broad leaves (Figure 2.1), while the potted plant grown in shade was spindly with just a few small narrow leaves at the top of the stem (similar to Figure 2.2, but more spindly, with fewer, smaller leaves). Bearing in mind that skipper caterpillars are often collected from vegetative plants under diverse conditions, the scope for doubt about species names for the food plant is clear. In spite of these challenges, we attempt to assess host specificity of the Hesperiinae Dracaena -feeders. There is not enough information to assess this for Gamia spp. as yet, whereas some Artitropa spp. seem to be generalists and others specialists.
Leaf extracts from Dracaena arborea have been shown to have insecticidal properties ( Udo 2013), and this may well be the case for the whole genus. SCC inadvertently found that cut leaves of D. steudneri placed in a box with caterpillars of Charaxes (Nymphalidae) led to their death. As a corollary, Dracaena spp. seem to be relatively free from insect attack. There are a small number of records of polyphagous Lepidoptera , including Homona mermerodes Meyrick (Tortricidae) in Papua New Guinea ( Hulcr et al. 2007), Amorbia emigratella Busck (Tortricidae) in southern USA and Central America ( Gilligan & Epstein 2012), Acharia stimulea (Clemens) (Limacodidae) in eastern North America ( Bibbs & Frank 2012), and Opogona sacchari (Bojer) (Tineidae) widespread in the tropics and subtropics ( Heppner et al. 1987), as well as several species not recorded from other host plants, but about which little is known: Amerila spp. ( Erebidae , Arctiinae ) in East Africa, Taenaris phorcas (Westwood) (Nymphalidae) in Australasia, and Eublemma rufimixta Hampson (Erebidae) in East Africa ( Robinson et al. 2010). There are also four genera of Hesperiinae incertae sedis which breed on Dracaena spp. The Afrotropical genera Gamia , Artitropa and one species of Leona are treated here, and are restricted to Dracaena spp., but Pirdana in South-East Asia also feed on Cordyline and Peliosanthes spp. ( Asparagaceae ) ( Piepers & Snellen 1910, Igarashi & Fukudu 1997).
TABLE 1. Dracaena spp. known to be used as food plants by Hesperiidae in mainland Africa; nomenclature and distribution of Dracaena spp. after Govaerts (2013); food plant records based on this paper.
? The identification of the food plant is in doubt, not that of the skipper.
* Records are from outside the natural range of these food plant taxa, so may represent misidentifications or exotic plants grown as ornamentals (see text).
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